msm: kgsl: Enhance preemption traces

Trace the value written to the CONTEXT_SWITCH_CNTL register
in order to know what preemption level was requested. Capture
and trace the value in CONTEXT_SWITCH_LEVEL_STATUS in the
preemption complete interrupt to know which level the CP
preempted. This is useful in performance and functional
analysis of the preemption feature.

Change-Id: If7ece9b39eadec80856bf7a3ad8a2c1653756cc7
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>